Background:

Originally I had 1LE fronts and 82-88 rear discs. Car was completely unable to lock the brakes even from a 25 mph roll. Pedal was hard with engine off, but suffered from (IMO) excessive pedal travel with engine running. Brake system was bled with regular DOT3 fluid. Original body lines, rear hoses, power booster; new front hoses, master cylinder, prop valve, front and rear calipers-pads-rotors.

Now I have the same 1LE fronts, but I also have the newer ('89-'92) rears. During the swap, I replaced the rear rubber hoses, rear calipers/pads/rotors, MC and PV (again), power booster, ALL body lines, flushed everything with alcohol, and used ATE super blue fluid.

I am STILL suffering from a complete inability to lock the brakes even from a 25 mph roll. Pedal is ROCK hard with engine off, but it still suffers from (IMO) excessive pedal travel with engine running.

I'm at my wits end with these brakes. Does anyone have ANY suggestions? The fact that it is rock hard with the engine off suggests a lack of power assist, but I replaced the booster (which was probably the original judging from the condition of it!!!!) without changing much.


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"Beware he who would deny you access to information, for in his heart, he dreams himself your master"

'84 Black Camaro ZZ4 M5 (V-6 in a former life) -- street beast
'91 Medium Blue Metallic Z28 A4 (UB-HSTRY's old ride) -- currently broken
'99 Navy Blue Metallic Firehawk #120 M6 (99.44% stock) -- daily driver

 

I have no advise for you I'm afraid but if it is any consolation your brakes sound just like mine. If you find out what is wrong, let me know!

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Cosmik Debris

 

This may sound stuipd but is the check valve installed correctly? If it was installed reverse it'd never give you power assist except a small burst at start-up.

 

How could you install it backwards? It looks like it only fits one way.

 

have you checked the vacuum hose from the manifold to the booster? just a though.

also, there is a procedure for adjusting the rear disk breaks. i have the instructions on this procedure if you are interested. i haven't scanned them yet but i can and then email them to ya.

are you saying you can't lock up the rears or all the brakes? i am assuming all the breaks from your post.

 

Yeah, I can't lock ANY of them.

Hmm here's a thought... since my car is not exactly stock, I don't have a metal line running from the carb... I think I'm using 5/8" heater hose. Could it be collapsing under vaccuum?

 

you might have a problem with the fact that you have a weak hose there. Im not sure what i replaced mine with, but i think it was heater hose.
let me ask you a few more questions, did you have this problem before you made your car non stock? dont know what cam you have but if it has alot of overlap, you could have insufficient vacuum. 2nd: have you checked you booster hose for cracks, leaks, etc.?
this may seem like a trivial, but i would pull the hose off while it is runnin and make sure there is vacuum there and if possible, stick a vacuum guage on it.

man i don't know what to tell ya, looks like you have really covered everything else that i could think of. i know my car doesnt stop the greatest with 4 wheel discs. of course, the 1LE's should be plenty of brakes.

 

99Hawk120,
I wish I could offer ome help but I have the same problem and out of ideas. Just about new everything front and back on a 1991 RS LO3 w/ 36,000 original miles and takes for ever to frigging shutdown in my opinion. I had two different shops look at it. Nothing seems to help. Of course they all say "Seems alright to me". Well yeah, if nobody pulls out in front of you or I have a football field to come to complete stop.
Later
Matt

 

Did you replace the master cylinder?? Just a thought but I know that alcohol dries out rubber seals and the master cylinder has many. I know stock replacements are cheap. Also is the proportioning valve the rite one for a car with rear disk??